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Has science shown that mind-body dualism is not a serious option?
Mind-body dualism is the view that we have both a mind and a body and that these are not the same thing, the mind being non-physical while the body is physical. This has been the predominant view in most people's thinking for most of history, taking the form of belief in something like a soul, usually an immortal one, in all religious worldviews. The most influential modern spokesperson to give philosophical arguments for mind-body dualism was Descartes. He claimed that the mind is a nonphysical substance capable of thought and experience, and that we are to be identified with this 'thinking stuff' rather than with our bodies, although our bodies and our minds are intimately related to each other: the mind is able to influence the body and the body is able to influence the mind. What links a particular mind with a particular body is that the mind can directly affect that body without affecting anything else, and vice versa. Descartes' arguments for dualism are now generally considered to be inconclusive. However, there is also the more serious problem that Descartes' form of dualism was inconsistent with certain physical laws, which leads to the question of whether any form of dualism could be consistent with science. The problem comes from mindbody interaction - specifically the influence of the mind on the body. Descartes was quite explicit about how he thought the mind and the body interacted. He decided it took place in the pineal gland, which seemed like a good candidate because it was unique and centrally located in the brain and its purpose was as yet unknown. Physical substances called 'animal spirits' flowed through the body in tubes, and as they went through the pineal gland, their direction and movement could affect the mind, and the mind could subtly change their direction of flow so as to bring about changes in the body. By saying that the non-physical self acted on the body only by altering the direction of the flow of animal spirits, Descartes was being consistent with an early form of 'conservation law' - the idea that the quantity of motion in the universe is never changed, but only redistributed among material bodies as they interact with each other upon impact. By only changing the direction of the animal spirits and not their speed, the mind was not imparting new motion to them. Unfortunately, modern conservation laws state that momentum does not change, and a body cannot undergo a change of direction without undergoing a change of velocity and hence momentum. So Descartes' interaction theory is inconsistent with modern science. This raises the question of whether any form of dualistic interaction could be consistent with science. Any such theory would have to posit a non-physical influence on the physical, presumably in the brain. As Hume pointed out, there is no reason a priori why we should find this implausible - however, as illustrated by the Descartes case, it looks as if there will be empirical difficulties. A theory of mind-body interaction will only be plausible if there is a meaningful place for it in our picture of how things work. But it seems very likely that our knowledge of the laws of physics is fully sufficient to account for the low-level workings of the brain in enough detail, in principle, poo! (by Mark Hogarth) to explain its functioning. So if any non-physical activity is meant to play a role in making the brain do what it does in fact do, it is entirely superfluous in our explanation of the phenomena - it plays no theoretical role. In order to do so - that is, to make any observable difference - it would have to violate
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